Road grade sensor

ABSTRACT

A vehicle wheel brake system in which vehicle and wheel speed signals are generated and utilized to generate a wheel brake pressure command signal, with the road grade sensor generating a signal reflecting the grade of the road on which the vehicle is moving. The road grade signal is used to further refine the command signal by taking into account the road grade. The system also senses brake torque and refines the command signal by considering the effect of changes in brake torque. The command signal controls mechanism, which, in turn, controls the wheel brake apply pressures.

United States Patent 11 1 [111 3,752,251

Gaeke 1451 Aug. 14, 1973 ROAD GRADE SENSOR 3,422.439 1/1969 Grubaugh73/516 [75] Inventor: Edward G. Gaeke, Dayton, Ohio [73] Assignee:General Motors Corporation,

Primary Examinerl(enneth 1-1. Betts Assistant Examiner-John McCormackDetroit Mich- Att0rney-W. E. Finken and D. D. McGraw [22] Filed: Aug.17, 1971 21 Appl. No.: 172,507 ABSTRACT Related s, Application Data Avehicle wheel brake system in which vehicle and [62] Division of No 883386 Dec 9 1969 PM No wheel speed signals are generated and utilized togener- 3632176 ate a wheel brake pressure command signal, with the roadgrade sensor generating a signal reflecting the 52 us. 01 180/104,73/514, 180/82 R grade of the road Oh which the vehicle is moving The 511 Int. 01 B60t 8/16 road grade Signal is used to further refine thecommand 58 Field of Search 303/21 cs, 24 A; Signal y taking into accountthe road grade- The y l88/181 73/514 516 R, 517 180/104, tem also sensesbrake torque and refines the command 103 82 signal by considering theeffect of changes in brake torque. The command signal controlsmechanism,

[56] References Cited which, in turn, controls the wheel brake applypres- UNITED STATES PATENTS 2,262,008 11/1941 Kollsman 73/514 2 Claims,10 Drawing Figures 3,588,188 6/1971 Shattock 303/21 CG 2,797,911 7/1957Montgomery 73/516 R FORWARD /y #W Patented Aug. 14, 1973 7 3,752,251

2 Sheets-Sheet 1 UP if 1 9 /a FORWARD W //l //6 w W 5w xii-E;

/ w A All a II y FORWARD //I w w I N VENTOR. Y [dz/0115 506% Li M 77ATTORNEY FORCE VS BRA KE I J g CONTROL FORCE VS ROAD GRADE 0 ROAD GRADEBRAKE TORQUE 2 Sheets-Sheet 3 VEHICLE SPEED F SPEED P,

SPEED 0,

FLYWHEEL DECELERATION NORMAL FORCE BRAKE TORQUE 5 PER CENT SLIP I FORCEVS SPEED VEHICLE WHEEL Patented Aug. 14, 1973 e m ma M/O 44 w M M PERCENT SLIP mDGmOP mvt mm A T TODNFY ROAD GRADE SENSOR This is a divisionof Ser. No. 883,386, filed Dec. 9, 1969, now US. Pat. No. 3,632,176.

The invention relates to a road grade sensor and more particularly to asensor for use in a vehicle wheel brake control system in whichwheel-to-road slip is controlled by various parameters including roadgrade. Systems of this type are commonly referred to as antilocksystems. The system in which the invention is disclosed ismechanical-hydraulic in nature, with a mechanical wheel speed sensor, amechanical vehicle speed simulator, a mechanical-hydraulic torquesensor, a mechanical-hydraulic road speed sensor, and amechanical-hydraulic wheel slip modifier.

It is a feature of the invention to provide means for generating asignal indicating the grade of the road on which the vehicle is movingto further refine the signal ultimately controlling vehicle wheelbraking.

The principal factors causing vehicle deceleration are the brakingeffort at the wheels, the wheel-to-road torque, and the grade of theroad on which the vehicle is moving. Systems of this type have beendevised and utilized which measure various parameters relating tobraking effort, wheel slip, and road surface conditions. In the parentapplication it was proposed to further refine such systems byconsidering the road grade. This is an important part of the overallconsideration of system operation when the grade varies to a significantextent. It is well known that vehicles being braked while ascending alarge grade may be braked more quickly, while vehicles descending alarge grade encounter the reverse braking situation. Road grades alsoaffect systems utilizing speed simulators. The best signal for modifyingsimulated vehicle speed is to obtain a good representation of actualspeed during braking. However, this signal is difficult to keep isolatedfrom vehicle pitch and road grade. Developed braking effort at thewheel, or wheel torque, provides another parameter which may be utilizedto modify a vehicle simulated speed signal and bring it in closerapproximation with actual vehicle speed. The road grade signal isutilized to counteract errors in vehicle speed acceleration which resultwhen substantial road grades are encountered.

In a preferred complete system utilizing the invention, road grade,brake torque and wheel speed are utilized. A simulated vehicle speed isgenerated and is modified by wheel brake torque and road grade. Thevehicle wheel speed signal and the vehicle simulated speed signal, asmodified, are combined and generate a wheel brake apply pressure commandsignal. This signal may also be modified by a wheel slip sensing deviceutilizing changes in brake torque to affect the command signal. Thecommand signal is presented as linear movement of a cam for controllingswitches, which, in turn, control valves of a wheel brake apply pressuremodulator, which, in turn, controls the application and release of wheelbrake pressure.

The road grade sensor embodying the invention claimed herein comprisesfirst and second gears in mesh with each other and an output gear inmesh with said first gear, the gears being mounted to rotate aboutparallel axes extending transversely of the vehicle, and first andsecond weights respectively secured to the first and second gears tomove therewith and extending in a vertical plane perpendicular to theparallel axes with like vertical components of extension and oppositeoutward components of extension. The road grade sensor is also providedwith an output signal generating means actuated by movement of theoutput gear to generate a road grade signal for use in the vehicle wheelbrake control system. The weights act to impress equal and oppositelyacting inertial forces on the first and second gears in response tovehicle acceleration and deceleration to maintain these gears in anunchanged equilibrium position. The weights also impress concurrentlyacting gravitationally caused forces on the first and second gears torotate these gears to a new position of equilibrium in response to achange in grade of the road on which the vehicle is moving andreflecting road grade through movement of the output gear.

In the drawings:

FIG. 1 is a schematic representation of a system utilizing theinvention, with parts broken away and in sectron.

FIG. 2 is a view of the road grade sensor contained in the system ofFIG. 1 and embodying the invention and showing the sensor in a modifiedposition due to change in road grade.

FIGS. 3, 4 and 5 show different positions of the switch operating camand the switches under different command signal conditions.

FIG. 6 shows the general characteristics and relationship between thecommand signal and the sensed speed and the wheel speed sensor and thevehicle speed sim ulator, the command signal being plotted as a force.

FIG. 7 shows the general characteristics and relationship between thebrake torque signal, plotted as a force, and the torque developed by thewheel brake.

FIG. 8 shows the general characteristics and relationship between theinertia wheel speed and the sum of forces acting on the vehicle speedsimulator modifier unit.

FIG. 9 shows the general characteristics and relationship between theanticipated road grade range and the road grade output signal generatedby the road grade sensor and shown as a force.

FIG. 10 shows the general characteristics and relationship between thecoefficient of friction, or brake torque, and percent of wheel slip forvarious road surface conditions.

The vehicle brake control system 10 of FIG. 1 is provided to control oneor more vehicle wheel brakes schematically illustrated as brake 12. Asource of brake pressure, such as master cylinder 14, is connectedthrough the wheel brake pressure modulator 16 to the wheel cylinder ofthe brake 12. Brake 12 may be a front wheel brake, a rear wheel brake,or any desirable combination thereof. The modulator 16 is controlled byvalves 18 and 20, which are electricallyactuated and are, in turn,respectively controlled by switches 22 and 24. Other than providing anoperative structure, the modulator 16, with its valves 18 and 20, formno part of the invention. The modulator may be hydraulically orpneumatically operated under the control of valves 18 and 20. Systemshaving modulators which may be utilized in practicing the invention aredisclosed and claimed in US. Pat. No. 3,592,514 issued July 13, 1971 toDeI-Ioff; and US. Pat. application Ser. No. 128,484, filed Mar. 26, I97I which is a continuation of US. Pat. application Ser. No. 806,807,filed Mar. 13, 1969 by Van Ostrom et al., now abandoned.

The control system components include the road grade sensor 26 to whichthe present invention is directed, the brake torque sensor 28, thevehicle speed simulator 30, the wheel speed sensor 32, the vehicle speedsimulator modifier 34-, the force accumulator link 36, the switch cam38, the force balance adjuster 40, and the percent slip modifier 42.Some of these components are circumferentially arranged about the axisof link 36, with only the upper portion being shown for simplicity.

The force accumulator link 36 is rotatably and slidably mounted in thebearing and guide 44, has a disc 46 on one end, a bearing retainer 48 onthe other end, and mounts the inner race of the thrust bearing 50. Theinner race of this hearing abuts retainer 48 and the outer race isprovided with a wear ring 52. The end of force accumulator link 36adjacent bearing retainer 48 forms a part of thrust bearing 50,schematically illustrated as including the center ball 54. Ball 54engages the end of the switch cam 38 so that linear force is transmittedbetween link 36 and cam 38, but not rotational force.

The frame 56 anchors the main support bearings 58 and 60 which supportthe wheel speed sensor 32. Sensor 32 includes a flyweight arrangement toproduce a force signal proportional to wheel speed. The sensor includesthe annular drive and inertia ring 62, to which are pivotably mountedflyweights 64. Only one such flyweight is shown. The flyweight includesa bellcranklike arrangement with the arm 66 having its end engaging thewear ring 52. As the flyweight 64 moves radially outward, it urges theforce accumulator link 36 to the right through arm 66 and thrust bearing50. A one-way clutch and bearing arrangement 68 is provided on the innerperiphery of ring 62, and includes inertia ring 70. This ring mountsbearing and guide 44. The outer periphery of ring 62 is formed as apulley and receives drive belt 72. This belt is suitably driven bythewheel associated with wheel brake 12; this construction beingschematically illustrated. in practice, other driving arrangements maybe made. Also, in some instances, the drive may be from the vehicledrive shaft which drives both rear wheels through the differential. Asused herein, the term wheel speed sensing is considered to besufficiently broad to include sensing rotational speed through suchdrive arrangements. Therefore, signals generated in accordance with orrelated to wheel speed are considered to include such variations.

Ring 70 is also a part of the vehicle speed simulator 30 and hasflyweights pivotably secured thereto, one such flyweight 74 beingillustrated. This flyweight is similar in construction to flyweight 64and includes a bellcrank arm 76, which has its outer end engaging thedisc 46 so that radially outward movement of flyweight 74 causes aleftward force to be exerted on force accumulator link 36 through arm 76and disc 46.

The one-way clutch and bearing unit 68 provides the means fortransmitting wheel accelerating motion to the vehicle speed simulatorand then allows the vehicle speed inertia ring 70 freedom to overrun thewheel speed sensor ring 62 when the wheel decelerates. A thrust bearing78 between a part of ring 70 and a part of ring 62 supports the reactionforce to the vehicle speed simulator signal. The vehicle speed simulatorperates to produce a force signal proportional to simulated vehiclespeed.

The overrunning action of inertia ring 70 will simulate vehicle speed sothat the simulated speed is approximately the same as actual vehiclespeed when the wheel is decelerated.

The vehicle speed simulator modifier 34 includes an annular brake disc80 which is provided with a suitable friction braking material 82, anannular friction plate 84 which is guided in axial movement by guidepins 86, and plate actuating means 88. The actuating means includes ahousing having cylinders and 92 formed therein and in which piston 94and 96 are respectively mounted for reciprocation. The pistons areconnected to plate 84 so that, as they are urged to the right bypressure in their respective cylinder, they increase the engaging forceacting on the plate against brake lining 82. As the force acting onplate 84 increases, the inertia ring 70 is caused to decelerate inproportion to vehicle deceleration caused by brake torque and the roadgrade over which the vehicle is operating.

in order to accomplish this, the brake torque sensor 28 is connected sothat its torque sensing input arm 98 acts through its piston 100 topressurize hydraulic fluid in its cylinder 102. Cylinder 102 is fluidconnected to cylinder 90 in a closed circuit so that an increase inpressure occurs in cylinder 90 in accordance with an increase inpressure in cylinder 102. Cylinder 102 is also fluid connected to thepercent slip modifier 42 as will be described.

The road grade sensor 26, embodying the invention herein claimed, actsto generate a pressure in its cylinder 104, which is fluid connected tocylinder 92 through a closed circuit so that the pressure in cylinder 92is in proportion to the pressure generated in cylinder 104. The piston106 of road grade sensor 26, acting in cylinder 104, is schematicallyillustrated as being moved by arcuate movement of arm 108 about the axis1 10 of the road speed sensor output gear 1 12. The road speed sensor 26also includes gears 114 and 116, respectively mounted for rotation abouttheir axes 118, 120. Gears 114 and 116 are meshed with each other, andgear 116 is meshed with gear 112. Thus, gear 112 follows arcuatemovement of the other two gears, and those other two gears are connectedto acttogether. The gear axes 110, 118 and are parallel to each otherand extend transversely of the vehicle in which the system is installed.This is indicated by the diagrammatic showing of the forward directionand upward direction of the vehicle. Gear 114 has a weight 122 securedto it, and gear 116 has a similar weight 124 secured to it. Theseweights are movable with their respective gears about axes 118 and 120in a vertical plane perpendicular to the gear axes and parallel to thevehicle center line. The weights have like vertical components ofextension; that is, they both have a downward component extension, asillustrated, or may both have an upward component of extension; and theyfurther extend with opposite outward components of extension. Thus,weight 122 has a rearward component of extension in relation to thevehicle and weight 124 has a forward component of extension in relationto the vehicle. It is preferable to attach the road speed sensor unit tothe vehicle axle to eliminate the effects of body deflection allowed bythe vehicle during deceleration. The sensor creates an hydraulicpressure signal in cylinder 92, in accordance with the grade of the roadon which the vehicle is moving. This pressure generates a force signaltransmitted through piston 96 to plate 84. This force signal modifiesthe simulated vehicle speed signal to compensate for the effect of roadgrade on vehicle deceleration. The road grade sensor weights 122 and 124act with equal and opposite torques on their respective gears 114 and116, resulting from the force of gravity on the weights. This results ina position of equilibrium in which there is no net torque output fromthe weights so long as there is no change in road grade. Vehicleacceleration and deceleration will not change the weight equilibriumposition since the weights experience equal and opposite inertia forcesin response to vehicle acceleration and deceleration. Therefore, thegears 114 and 116 are maintained in the unchanged equilibrium position.

When the road grade changes to an upward grade, the torque output ofweight 124 increases while the torque output from weight 122 decreasesbecause of the change in effective torque arm length, assuming thevehicle to be traveling in a forward direction up the grade. Thisresults in a torque imbalance transmitted through gear 116 to outputgear 112, arm 108, and piston 106 to increase the hydraulic pressure incylinders 104 and 92. When the vehicle is being driven forwardly andencounters a descending road grade, the reverse situation occurs and theresulting torque imbalance is transmitted to cause a decrease inpressure in cylinders 104 and 92. Thus, the amount of force generated bypressure in cylinder 92, and acting on plate 84, varies in accordancewith the road grade. The road grade signal causes an increase in brakingforce on lining 82 when an ascending grade is encountered, therebymodifying the simulated vehicle speed signal to account for the fastervehicle speed deceleration under such circumstances.

The percent slip modifier 42 includes a housing 126 with a chamber 128and a power wall 130, sealing one end of the chamber. The chamber isfluid connected to the closed hydraulic system of the brake torquesensor 28 through conduit 132. Therefore, the pressure signal indicatingbrake torque, generated in cylinder 102, is delivered to move the powerwall 130. A push rod 134 is connected to be moved by power wall 130 andhas its outer end engaging the end of force accumulator link 36 on whichdisc 46 is provided. Thus, the percent slip modifier utilizes the braketorque signal to modify the summation of the simulated and modifiedvehicle speed signal and the wheel speed signal as they are applied tothe force accumulator link.

The force balance adjuster 40 includes a compression spring 136 engagingthe end of switch cam 38 opposite torque bearing 54 and a springcompression force adjuster, illustrated as adjusting screw 138. Thecompression force of spring 136 is adjusted to balance the forceaccumulator link so as to properly index the switch cam.

The switch cam includes a pair of lands 140 and 142 separated by abeveled groove 144. Switch 22 has a cam follower 146 and switch 24 has acam follower 148. These followers are in engagement with the cam 38 andride on either land 140 or land 142 or in groove 144. As is moreparticularly shown in FIG. 3, when the system is in the brake pressureapply condition, both switches 22 and 24 are held open since their camfollowers 146 and 148 are both in engagement with cam land 140.

When the command signal generated by the system is such that the forceaccumulator link moves leftwardly to require a brake pressure releaseposition, it moves through the brake pressure slow apply position ofFIG. 4 to the brake pressure release position of FIG.

5. In the brake release position, cam follower 146 is in groove 144 sothat switch 22 is closed. Cam follower 148 engages land 142 so thatswitch 24 is open. In this condition, valve 18 will be open while valve20 will be closed, controlling the modulator 16 to release wheel brakeapply pressure delivered to the brake 12. When the force accumulatorlink 36 moves cam 38 rightwardly from the brake pressure releaseposition, it establishes the brake pressure slow apply position of FIG.4 in which switch 22 is open and switch 24 is closed. This causes themodulator 16 to slowly apply the brake apply pressure. Further rightwardmovement of the force accumulator link 36 and of cam 38 returns thesystem to the brake pressure apply position shown in FIG. 3. In thisposition, pressure from the master cylinder 14 is delivered to the brake12.

The graphs of FIGS. 6 through 10 relate the output signal to thegenerating parameter. The curves are provided as examples, and curvesfor any particular hardward may vary somewhat, but will follow thegeneral pattern set forth. The output signals are illustrated as forcesplotted against speed in FIG. 6. Curve 150 indicates the force signalobtained from the vehicle wheel speed sensor 32. Curve 152 indicates theforce signal generated by the vehicle speed simulator 30. Curve 154 ofFIG. 7 indicates the force signal generated by the brake torque sensor28. Curve 156 of FIG. 8 plots flyweight deceleration against the forcesignals acting through the vehicle speed simulator modifier 34. Curve158 of FIG. 9 plots the force signal of the road grade sensor through arange of road grades from a 27% descending grade to a 27 percentascending grade. Curves 160, 162, 164 and 166 plot brake torque againstthe percent slip of the wheel to the road surface with four differentroad surface conditions. These conditions relate to a dry concretesurface; a wet road surface; a road surface covered with snow, and anice covered road surface. These four curves have been well establishedin the prior art.

The operational sequence occurring in the system will now be described.In the normal condition of operation of the vehicle brake system, thecam 38 is in the position shown in FIG. 3 and the vehicle brakes operatewithout being affected by the control system. When the vehicle is drivenon a road at a steady speed, the vehicle speed inertia ring and thewheel speed inertia ring 62 will be driven at the same speed. The wheelspeed ring 62 drives the vehicle speed ring 70 through the one-wayclutch 68. The force signals generated by these two sensors are equaland, therefore, the force exerted in opposite directions on forceaccumulator link 36 are equal and opposite. In this force balancecondition, with the brakes being released, spring 136 holds the forceaccumulator link 36 and the cam 38 in the brake apply positionillustrated in FIG. 3. When the vehicle brakes are applied, the vehiclewheel, to which wheel speed sensor is operationally connected by belt72, decelerates. This causes a deceleration of ring 62 and flyweights64. However, by action of the one-way clutch 68, the vehicle speedsimulator ring 70 overruns due to its inertia. The control force balancetherefore changes with this differential in speed between the two speedsensor units, tending to move the force accumulator link 36 leftwardly.In addition, the brake torque sensor 28 generates a brake torque signalacting through piston 94 and the vehicle speed simulator modifier 34 todecelerate the ring 70 in accordance with brake torque, causing anotherforce signal change.

The comparison of these force signals results in a While in the abovedescription reference is generally command signal generatedas a forcesignal transmitted made to sensing speeds, it is also within the scopeof the from the force accumulator link to switch cam 38, and disclosureto sense decelerations and accelerations and spring 136 moves the wit ham lefzwa dl when th to utilize signals of this nature. Such signals aretherepercent slip, or wheel speed separation from vehicle fore alsoreferred to as movement characteristic sigspeed, is sufficiently large,cam 38 will be located in the nals. The invention is disclosed as a partof a mechanibrake pressure slow apply position shown i FIG 4,cal-hydraulic system,but may also be practiced in com- The slow applybrake ressure will all a d l i bination with other types of sensing andsignal accumucrease in brake effort which will also increase the brakelating Combining devices- The nts of the C H- torque developed and thusincrease the force signal 10 System y be electrical, Pneumatic orhydraulic. generated by the brake torque sensor. This increased aCombination thereof- The yp of hi aking signal acting on the vehiclespeed simulator 30 through System in which the invention is utilized ybe Olhef the modifier 34 will offset the decreased force signal than thehydraulic syslem Sehemaueahy illustrated, accomplished by the decreasein wheel speed as sensed Such as Positive Pressure electrical, orelectromagby wheel speed sensor 32. This will continue until the helle hnature It is y in its more Speelfic aspects, as wheel-to-road torquecannot be increased. This point Particularly disclosed and Claimedherein, that occurs t h hi h peint of h appropriate curve f theinvention applies to a mechanical road grade sensor FIG. 10. Beyond thispoint, the vehicle wheel will have in a mechanical System a largedeceleration and brake torque will also de- What is claimed is: crease.The force balance will shift, causing the force For use in a Vehicle, aroad grade Sensor p accumulator link 36 to be moved further leftwardlyby 8 the command signal until the switch cam 38 is in the first andsecohfl gears mesh y each Other and brake release position of FIG. 5.This will further re- -P gear mesh with Sam first gear, 531d gears ducethe brake torque and will allow the vehicle wheel bemg mounted to rotateabout Parallel axes to accelerate. When the wheel speed has increasedsuftending trahsyel'sely of the Vehicle; ficiently to develop asubstantially large force signal by and first and Second Weightsrespectively Secured he ans f h wh l Speed Sensor to again change h saidfirst and second gears to move therewith, said command signal, the forceaccumulator link 36 and the Weights extending in a Vertical PlanePerpendicular cam 38 will be moved to the ri ht, and m 38 will to saidaxes with like vertical components of extensume either the slow apply orthe full apply position desion and opposite outward components ofextenpending on the magnitude of the signal, which, in turn, sion;depends on the magnitude of the speed differences. said weightsimpressing equal and oppositely acting Control of the deceleration ofthe inertia ring 70, utiinertial forces on said first and second gearsin relized to simulate vehicle s eed, is regulated b th spouse tovehicle acceleration and deceleration to amount of force exerted throughthe modifier 34. In adntain aid g ars in an unChanged equilibrium ditionto the brake torque force signal, the road grade position, andimpressing concurrently acting gravisensor 26 generates another forcesignal acting through tationally caused forces on said first and secondpiston 96 and brake plate 84. By combining brake gears to rotate saidgears to a new position of equitorque signals and road grade signals,the vehicle speed librium in response to a change in grade of the roadsimulator ring 70 is decelerated to provide a good ap- 40 on which thevehicle is moving and reflecting road proximation of actual vehiclespeed. Furthermore, the grade through movement of said output gear.percent slip modifier acts in accordance with changes 2. For use in avehicle wheel brake control system to in brake torque to modify thesummation of signals modify braking action in accordance with thechanges from the wheel speed sensor 32 and the vehicle speed in grade ofthe road on which the vehicle is moving, a

simulator 30, as modified through modifier 34, to furroad grade sensorcomprising. ther refine the command signal. first and second gears inmesh with each other and an The following charted information provides aready output gear in mesh with said first gear, said gears comparison ofconditions of various elements of the being mounted to rotate aboutparallel axes exsystem under each condition of operation. tendingtransversely of the vehicle;

Master cylindcr pressurized Master cylindcr Brakes1 applied Brakesapplicdwliecl Unit or signal released norm slipping Brakes releasedBrakes released Vehicle wheel speed (8;) Steady state. DecclerateDccelcratc Accelerate Decelerate. Vehicle speed (5:) do do doDecelcrating. Do. Vehicle srpeed control force 5' signal( 2) S1=S2 sl=S2sl s2 S 2 si s:. Vehicle wheel s eed control 01138 signal (F1 F F2 F1 F:F1 F2 FI F2 F1 F2. Wheel brake torque control 0 Increasing Steady todecreasing Decreasing Decreasing.

force signal (Fa). Command signalsummal- O ticn of control force signalsr 2-ls) Vehicle speed simulator fly- Zero. Zero or increasing. Veryslowly increasing Decreasing Decreasing.

wheel braking torque Response rate. Fast Fast Gradually Fast Fast.Switch cam posit To right To right Center 'Ioleft To left. Switchcondition:

Switch 24"". 013011.. s Closed O on Open. Switch 22. -do. d on C oscdClosed. Modulator hydraulic section" Open to 1nd or Open ton C used tomaster cylinder Closed to master L) n Closed to master cylincylinder.cylinder or and increasing pressure or dcr and decreasing den anddecreasing increasing moving toward reopening pressure or movingpressure or moving pressure. to master cylinder prcstoward valveclosing. towardvnlvcclosing.

surc. Brake apply pressure None Increasing. Gradually incrcnsing..Decreasing Decreasing. Brake torque .do do d0 d D0.

said weights impressing equal and oppositely acting inertial forces onsaid first and second gears in re sponse to vehicle acceleration anddeceleration to maintain said gears in an unchanged equilibriumposition, and impressing concurrently acting gravitationally causedforces on said first and second gears to rotate said gears to a newposition of equilibrium in response to a change in grade of the road onwhich the vehicle is moving and reflecting road grade through movementof said output gear.

@lnventor s) UNITED STATES PATENT OFFICE Patent No. 3.152 .253 Dated Itis certified that error appears in the above-identified patent and thatsaid Letters Patent are hereby corrected as shown below:

MASTER CYL ER ssusuzxb Broken mate: Brakes Applied- Cylinder Applied-Wheel Brakes Bx'ekee Unit 0: Signal Releeeed Normal Sligging ReleaeedReleased Vehicle wheel Speed I (5 Steady State necelente DecelezeteAccelerate Decelezete Vehicle Speed (S Steady sac. Decelente DecelenteDecelereting Oeceletete Vehicle Speed Conn-cl Force Signal (F VehicleWheel Speed control Force siqnel v (P '1 v P 72 I I: 11 I '2 Wheel BrakeTorque Control Force Signel 0 xnczeeeinq Steady to Decreeeing Decreeeinqdeczeeeinq Command Signal Sumnation of Control Force Signale (F -2 41'.1- 0 Vehicle Speed Simulator f Flywheel Braking Torque zero zero orVery elowly Decreeeinq Deczeninq increeeinq incteeeing Relpoaee RateFeet Feet Gradually Pee: I'eet Switch can Poeition To right To rightCenee: fro left To lett switch Condition Switch 24 Given open Clonedopen Open switch 22 Open Open open closed Cloeed Modulator HydraulicOpen to mete: open to Meete: Closed to Mute: Cloned 1:0 Mute: ClOled toMaster Section Cylinder Cylinder 0: Cylinder end in- Cylinder end de-Cylinder end deincl-peeing cren-ing pressure creeeing pzeeeuze czeeeingpreeeure pteeeure or moving coverd or moving wuetd or moving tovezdreopening co valve cloeinq velve cioeinq Maeter cylinder pteeeure BrekeApply Pteeeute None Incz'eeeinq Gnduelly Decreeeinq Deczeuinqinci'eeeing Bteke Torque None Indteeeinq Gnduelly Decteeeinq Decteeeinqincreeeinq Signed sealed this 11th day of February 1975.

(SEAL) Attest:

C. MARSHALL DANN" Commissioner of Patents and Trademarks RUTH C. MASONAttesting Officer FORM PO-1050 (10-69) USCOMM-DC 60376-P69 w u.s.sovznunzur rnm'rmc OFFICE uses 0-366-31".

1. For use in a vehicle, a road grade sensor comprising: first and second gears in mesh with each other and an output gear in mesh with said first gear, said gears being mounted to rotate about parallel axes extending transversely of the vehicle; and first and second weights respectively secured to said first and second gears to move therewith, said weights extending in a vertical plane perpendicular to said axes with like vertical components of extension and opposite outward components of extension; said weights impressing equal and oppositely acting inertial forces on said first and second gears in response to vehicle acceleration and deceleration to maintain said gears in an unchanged equilibrium position, and impressing concurrently acting gravitationally caused forces on said first and second gears to rotate said gears to a new position of equilibrium in response to a change in grade of the road on which the vehicle is moving and reflecting road grade through movement of said output gear.
 2. For use in a vehicle wheel brake control system to modify braking action in accordance with the changes in grade of the road on which the vehicle is moving, a road grade sensor comprising: first and second gears in mesh with each other and an output gear in mesh with said first gear, said gears being mounted to rotate about parallel axes extending transversely of the vehicle; first and second weights respectively secured to said first and second gears to move therewith, said weights extending in a vertical plane perpendicular to said axes with like vertical components of extension and opposite outward components of extension; and an output signal generating means actuated by movement of said output gear to generate a road grade signal for use in the vehicle wheel brake control system; said weights impressing equal and oppositely acting inertial forces on said first and second gears in response to vehicle acceleration and deceleration to maintain said gears in an unchanged equilibrium position, and impressing concurrently acting gravitationally caused forces on said first and second gears to rotate said gears to a new position of equilibrium in response to a change in grade of the road on which the vehicle is moving and reflecting road grade through movement of said output gear. 